Polychlorinated biphenyls, or "PCB's" were, long used as dielectric fluids in electrical equipment because these materials have excellent heat stability, are non-flammable in nature, have low volatility and a good viscosity characteristic at operating temperatures. Because of their environmental persistence, however, continued manufacture, import, or use in the United States was banned under the Toxic Substances Control Act of 1976, and the U.S. Environmental Protection Agency was directed to promulgate rules and regulations for their removal from the economy.
As of July 1, 1979, EPA regulations define as "PCB-contaminated" any material containing more than 50 ppm of a mono-, di-, or polychlorinated biphenyl. The regulations permit disposal of PCB-contaminated materials by either incineration in an approved manner or in an approved landfill, but such procedures have rarely proven acceptable to community neighbors. Since considerable fractions of the transformer oils, e.g., refined asphaltic-base mineral oil, or heat exchange oils, e.g., hydrogenated terphenyls, now in serivce are PCB-contaminated, the problem of disposing of PCB-contaminated hydrocarbon oils in an effective manner presents a serious challenge. As used hereinafter, the term "transformer oil" signifies a mineral insulating oil of petroleum origin for use as an insulating and cooling media in electrical apparatus, for example, transformers, capacitors, underground cables, etc.
Various techniques for meeting this challenge have been proposed. One method is shown by D. K. Parker et al, Plant Engineering, Aug. 21, 1980, Pages 133-134. The method of Parker et al is based on the formation of a solution of an organo-sodium reagent, such as sodium naphthalenide, in a carrier solvent, for example, tetrahydrofuran, which is then added to the contaminated oil. The Parker et al process requires a multistep procedure involving first the formation of organo-sodium reagent, next the incorporation of such organo-sodium compound into the PCB-contaminated oil followed by at least 2 more hours for the reaction to be complete, followed by a water quench and distillation and purification steps to recycle the tetrahydrofuran. Another procedure, somewhat similar to the Parker et al process, is described by Smith et al, University of Waterloo, based on the graduate thesis of James G. Smith and G. L. Bubbar, "The Chemical Destruction of Polychlorinated Biphenyls by Sodium Napthalenide". Again, a lengthy, multistep procedure is necessary before effective destruction of the PCB is achieved. A further procedure is shown by Hiraoka et al, Japan Kokai 74 822,570, Chem. Abstracts 89831K, Vol. 82, 1975, which describes the destruction of polychlorinated biphenyls utilizing a sodium dispersion in kerosene, but requires a 6 hour heating period at 120.degree. C.
The present invention is based on the discovery that destruction of PCB's can be achieved directly without the necessity of preforming an organo-sodium reagent, by adding finely divided sodium metal directly into PCB-contaminated transformer oil along with a suitable organic electron carrier, such as benzophenone, biphenyl, naphthalene, etc., and an aprotic ion-solvating solvent, such as diglyme, or tetrahydrofuran, etc., while agitating the mixture under an inert atmosphere. The direct addition of finely divided sodium metal to the PCB-contaminated mixture eliminates the several hours of processing required in making the preformed sodium complex. Further, the direct addition of the organic electron carrier and aprotic ion-solvating solvent along with the sodium metal has been found to significantly reduce total reaction time, limit the requirements for ion-complexing solvent to the point where the solvent recovery and recycling steps are unnecessary, and to permit the reaction to be carried out at ambient temperatures.